I own a PCchip 748LMRT
I believe it is the same motherboard, but mine has higher revision
In either case, the fastest you can use is the PPGA Celeron, which goes as high as 500mhz I believe ???
Or you can find a cheap Celeron 366 here and OC it ot 550 using the 100mhz bus.
ps. you need to flash the newest bio, if there is such a thing